题目下列运算中，错误的是( )A.x−yx+y=−y−xy+x\dfrac{x-y}{x+y}=-\dfrac{y-x}{y+x}x+yx−y=−y+xy−xB.−a−ba+b=−1\dfrac{-a-b}{a+b}=-1a+b−a−b=−1C.(1−2)2=2−1\sqrt{{{(1-\sqrt{2})}^{2}}}=\sqrt{2}-1(1−2)2=2−1D.a2=a\sqrt{{{a}^{2}}}=aa2=a知识点：分式的基本性质,二次根式的非负性章节：未标注
